As shown by Banucci et al U.S. Pat. No. 4,098,800, assigned to the same assignee as the present invention, particulated oligomeric polyetheramide acids can be made by effecting reaction between (a) an aromatic bis(ether anhydride) of the formula, ##STR1## and (b) mixtures of one or more of said bis(ether anhydride)s with up to 30 mole percent benzophenone dianhydride of the general formula, ##STR2## with at least one organic diamine of the general formula, EQU (3) H.sub.2 N-R-NH.sub.2,
in an inert organic liquid selected from the group consisting of (c) chlorinated hydrocarbon selected from the group consisting of methylene chloride, chloroform, 1,2-dichloroethane, and mixtures thereof and (d) mixtures of said chlorinated hydrocarbon with up to 50% by weight of acetone to form oligomeric polyetheramide-acid which is substantially insoluble in said liquid, where Z is a member selected from ##STR3## and divalent organic radicals of the general formula, ##STR4## where X is a member selected from the class consisting of divalent radicals of the formulas,
--C.sub.y H.sub.2y --, ##STR5## --O-- and --S--, where y is an integer from 1 to 5, and R is a divalent organic radical selected from the class consisting of aromatic hydrocarbon radicals having from 6 to about 20 carbon atoms and halogenated derivatives thereof, alkylene radicals having from 2 to about 20 carbon atoms, cycloalkylene radicals having from 3 to about 20 carbon atoms, from C.sub.2 to about C.sub.8 alkylene terminated polydiorganosiloxane and divalent radicals of the general formula, ##STR6## where Q is a member selected from the class consisting of --O--, --S--, and --C.sub.x H.sub.2x --, where x is an integer from 1 to 5. PA1 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride; PA1 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride; PA1 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride; PA1 4,4'-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride; PA1 4,4-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride; PA1 2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride; PA1 4,4'-bis(2,3-dicarboxyphenoxy)diphenyl ether dianhydride; PA1 4,4'-bis(2,3-dicarboxyphenoxy)diphenyl sulfide dianhydride; PA1 4,4'-bis(2,3-dicarboxyphenoxy)benzophenone dianhydride PA1 4,4'-bis(2,3-dicarboxyphenoxy)diphenyl sulfone dianhydride; PA1 4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)-diphenyl-2,2-propane dianhydride, and mixtures thereof. PA1 o-phenylenediamine, PA1 m-phenylenediamine, PA1 p-phenylenediamine, PA1 4,4'-diaminodiphenylpropane, PA1 4,4'-diaminodiphenylmethane (commonly named 4,4'-methylenedianiline), PA1 4,4'-diaminodiphenyl sulfide (commonly named 4,4'-thiodianiline), PA1 4,4'-diaminodiphenyl ether (commonly named 4,4'-oxydianiline), PA1 1,5-diaminonaphthalene, PA1 3,3'-dimethylbenzidine, PA1 3,3'-dimethoxybenzidine, PA1 2,4-bis(.beta.-amino-t-butyl)toluene, PA1 bis(p-.beta.-amino-t-butyl)ether, PA1 bis(p-.beta.-methyl-o-aminopentyl)benzene, PA1 1,3-diamino-4-isopropylbenzene, PA1 1,2-bis(3-aminopropoxy)ethane, PA1 benzidine, PA1 m-xylylenediamine, PA1 p-xylylenediamine, PA1 2,4-diaminotoluene PA1 2,6-diaminotoluene, PA1 bis(4-aminocyclohexyl)methane, PA1 3-methylheptamethylenediamine, PA1 4,4-dimethylheptamethylenediamine, PA1 2,11-dodecanediamine, PA1 2,2-dimethylpropylenediamine, PA1 octamethylenediamine, PA1 3-methoxyhexamethylenediamine, PA1 2,5-dimethylhexamethylenediamine, PA1 2,5-dimethylheptamethylenediamine, PA1 3-methylheptamethylenediamine, PA1 5-methylnonamethylenediamine, PA1 1,4-cyclohexanediamine, PA1 1,12-octadecanediamine, PA1 bis(3-aminopropyl)sulfide, PA1 N-methyl-bis(3-aminopropyl)amine, PA1 hexamethylenediamine, PA1 heptamethylenediamine, PA1 nonamethylenediamine, PA1 decamethylenediamine, PA1 bis(3-aminopropyl)tetramethyldisiloxane, PA1 bis(4-aminobutyl)tetramethyldisiloxane, and mixtures of such diamines.
It has been found that the above-described particulated polyetheramideacids of Banucci et al are useful in various coating applications, for example, applications to aluminum or copper wire using fluid bed electrostatic coating procedures. However, these electrostatically applied oligomeric powders can readily form films containing entrapped bubbles which reduce the insulating characteristics of the polyetherimide coating. It has now been discovered that substantially bubble-free films can be made by preheating the particulated, substantially organic solvent-free polyetheramide acid, preferably in an oxygen-free atmosphere and at a temperature in the range of 135.degree. C. to 175.degree. C. for a period of time sufficient to effect at least 70% imidization of the organic solvent-free polyetheramide acid without causing a substantial degree of sintering or agglomeration of the polyethermide powder. This result is quite surprising since the imidization of the particulated polyetheramide acid occurs in the absence of an organic solvent.